Tube flash

Thanks everyone very much for your comments. It was a power tube, coincidentally an EL34, as mentioned by Steveaustin. I did try the tapping test and saw no flicker in the testing lamp, and no, I did not put the tube back in the Amp after I tested it. I’ve replaced the tube and fuse and have 10-15 hours on the amp since replacing. So it does not appear to be a problem inside the amp, at least a problem that manifesteds itself right away.

Just to take it to the next level though, this is the fourth of eight EL34 Winged C tubes that has blown in the amps (they’re monoblocks) in the last two years. The tubes started blowing within the first 200 hours of usage. The tubes still have less than 1000 hours of service and all test in the good range on my tester. The tubes were purchased from a very reputable dealer. The tubes were all matched. The amps are Conrad Johnson Premier 12’s. The tubes have blown in both amps. I’ve taken the amps back to Conrad Johnson twice for testing (I live in the area). Each time they say no problems with the amps, just a bad tube.

Anyone have any ideas?

Rodman, funny you should mention Upscale because that’s where these tubes were purchased. I guess it’s the luck of the draw, and in my case, my draw was aces over sevens.

And Newbee, you have an interesting premise. I should have mentioned though that my amps are the Premier 12 XS, which are configured to use EL34’s. So I assume the bias circuit is designed around EL34’s, but I’m going to ask Conrad Johnson that exact question. It’s also interesting that the last time I was at Conrad Johnson, I bumped into Lew Johnson and asked him what he though might be going on. His first question was what type of speakers are you using. When I told him Quads (63’s), he commented that they (Conrad Johnson) had some previous problems with customers that used Quads and their amps. He said that the Quads, under certain circumstances might draw too much current. This all sounded a little strange to me (I was always told Quads and tubes were a good match) but I’m not an electrical engineer and he was talking a little over my head, so I may have misunderstood. Since then I’ve taken the Quads out of service, and I’m using dynamic speakers. But the problem has continued.

Thanks again for everyone’s comments. Any other thoughts would be very much appreciated

"How old was the tube that failed? Have you contacted Kevin in regards to the tube's failure (and possible warranty)? Did the same thing happen more than once? You mentioned, "the problem has continued”

No I haven’t contacted Upscale…the first tube that failed was probably 4 – 6 months old. As I mentioned before, this is the fourth of eight tubes that has failed. I should have taken notes, so I really don’t remember when the tubes failed, which positions failed, etc. I do know it has happened in both amps.

"(why I ask)".

“Why” the problem continues is what I am wondering as well.

"Next time you talk to CJ ask them what the bias setting programmed into the amp actually is. After they tell you ask them what the bias setting is in the 6550 model. Then find out if they actually checked the bias in your amps with your tubes in it as opposed to just noting the tubes and the little LED were working."

Now that I know a little more specifically what to ask, I will. Thanks for the advice. I do know that they checked the bias in the amps with my tubes the last time they were in for service. That’s how they found the problem (the amp was blowing fuses and my tester was not detecting a bad tube).

"If you have a techie nearby you might ask him to check and see what the bias actually is."

Actually, Bill Thalmann, whom I believe may have designed the Premier 12’s when he worked for CJ, also has his shop in my area. So I may take it to him the next time it happens.

Unless I'm on the wrong site I see no reference to what you refer to. Can you give me a link?

Hifitime, thanks for the link. Interesting, but my (limited) experience with tubes is the same as yours.